The present invention relates to the detection of persons trapped in mining disasters or building or other structural collapses caused by earthquake or other destructive forces. More particularly, the invention relates to seismic instrumentation structured to provide improved detection of tapping signals made by a trapped person who has survived a disaster.
In 1989, a study was made of existing seismic sensors and signals like those occurring at structural disaster locations to determine how to facilitate differentiation of ambient seismic noise from tapping or similar signals. In the study, ambient noise typically caused the seismic sensor to generate a low frequency oscillatory or ringing signal, typically about 30 Hz. The exact value of the ambient signal frequency will vary according to the particular seismic sensor employed and other factors.
A simulated discrete tapping signal, such as that which would be caused by a survivor's foot tapping on the ground, typically caused momentary detected signal components of about 22 Hz to 44 Hz. However, the tapping signal may vary in frequency within a relatively narrow low frequency range, and further it may be difficult to detect because of the strength of the ambient noise.
The present invention is directed to resolving this detection problem by providing a seismic detection system in which characteristic survivor tapping signals are enhanced relative to ambient noise signals to provide greatly improved detection capability.